Retractable assemblies are sold by the group of firms, Endress+Hauser, in great variety, for example, under the designation “Cleanfit H CPA875.”
Retractable assemblies are used widely in analytical measurements technology and process automation. They serve to withdraw and reintroduce probes out of and into a process, and thus a medium, without process interruption. The probes are secured in an immersion tube and moved by means of a drive manually or automatically, for example, pneumatically, axially between a process position (measuring) and a service position (maintenance, calibration, washing, probe exchange, etc.). These procedures run within a certain timing cycle or as a function of other determinable or measured parameters.
Probes in the sense of this present disclosure include probes with at least one accommodation for at least one sensor for measuring one or more physical or chemical, process variables.
The scope of use of retractable assemblies for measuring physical or chemical, process variables of a medium, e.g. a fluid, especially a liquid, in process technology is broad. Used for determining the process variables are sensors, such as pH-sensors, conductivity sensors, optical or electrochemical sensors for determining a concentration of a substance contained in the medium to be monitored, e.g. O2, CO2, certain ion types, organic compounds, or the like.
If retractable assemblies are used for accommodating the sensor for determining at least one process variable, the sensor can be checked, calibrated, cleaned and/or replaced in the service position, wherein the sensor is located, in such case, in the housing interior of the retractable assembly, in the so-called service chamber. In order that the medium not be contaminated by the calibration, rinse or cleaning liquid, in the service position, the service chamber is so sealed from the containment, in which the medium is located, that no exchange of medium/liquid can take place. Usually for this purpose, there is located on the media end of the housing of the retractable assembly a seal, which in interaction with the end region of the immersion tube prevents an exchange of medium/liquid. A seat for the seal is located in the immersion tube or in the housing (i.e., service chamber). Used as seal is frequently an O-ring or a shaped seal. The groove for the seal is, in such case, rectangularly shaped in cross section. In such case, gaps frequently arise when the seal is in place.
The gaps and edges form dead spaces, where particles can deposit and scale and/or biofilms can form. These are undesirable, since they degrade the functional ability of the retractable assembly. In the worst case, germs and the like can collect, multiply and so contaminate the medium and make it unusable.
DE 10 2013 111 057 A1 discloses a sealing system and a retractable assembly, which satisfy hygienic requirements. Different hygiene regulations require different types of assembly construction.